The present invention relates to spring energized fastening tools. More precisely, the present invention relates to improvements to the spring and release of a spring-actuated stapling device.
Spring powered staplers and staple guns operate by driving a striker with a power spring. The striker ejects a staple by impact blow. In a desktop stapler, the staple is ejected into an anvil of a pivotally attached base. In a staple gun, the fastener is normally installed directly into a work surface. Two general principles are used in either type device. In the first design, the striker has an initial position in front of a staple track. The striker is lifted against the force of the power spring to a position above the staple track. The striker is released to impact and eject the staple. This design may be referred to as a “low start” stapler. A second design uses a “high start” position. That is, the striker has an initial position above the staples loaded on the staple feed track. The power spring is deflected while the striker does not move. At a predetermined position of the power spring deflection, the striker is released to accelerate into and eject a staple. A handle normally serves as an energy input device although motorized versions need not have a handle. Spring energized staple gun tackers have traditionally used a low start configuration although high start type tackers are known. Spring energized desktop staplers of both types are currently available.
In both high and low start types, the power spring can be made of wire or have a flat metal shape. The flat metal types are normally elongated along a length of the body. Wire springs may be horizontally elongated or vertically oriented compression style. Modern designs tend toward the elongated type, for example a torsion spring with extended arms.
A limitation of conventional designs is the absence of simplified structures to preload a torsion spring in a high start type. Further, an improvement is called for in providing a more compact lever arrangement to operate with the simplified wire spring.
In comparing a flat spring to a wire spring design, the length tolerance of an elongated flat spring is relatively precise, being limited mostly by the precision of the blank cut out for it, in the case that the spring is of reasonably straight bend. For a wire spring, however, the arm length may be less precise since it depends on the manner in which the coil is wound among other factors. It is therefore desirable to have a release mechanism that is less sensitive to spring length with a high start type wire spring.